Chemisty Question See Description

Question

A solution contains 8.10×10^-3 M sodium carbonate and 8.97×10^-3 M ammonium fluoride. 

Solid barium nitrate is added slowly to this mixture. 

What is the concentration of carbonate ion when fluoride ion begins to precipitate? 

[carbonate] =  M 

Answer 1

CO3^2-(aq) + 2F^-(aq) + Ba²⁺(aq) ==> BaCO₃(s) + BaF₂(s) ... net ionic

In order to answer the question as posed, I believe one would need to know the Ksp for BaCO₃. Otherwise, I can't see how to approach this problem.